Robust Optimal Designs of Fiber Reinforced Composite Structures with Uncertainties
Date Issued
2008
Date
2008
Author(s)
Chiou, Chwei-Yuh
Abstract
Fiber reinforced composite material is composed of many plies. The problem of optimal design of composite structure is to select the proper ply arrangements so as to achieve the highest performance for the specified requirement of strength, stiffness or other mechanical properties. Due to the uncertainties in material properties and the variations of ply thickness and ply orientation in manufacturing, the practical design properties can be different from what the designers predict. Robust optimal design techniques such as anti-optimization method and probabilistic optimal method are frequently used to deal with the optimal design problems of composite structures with uncertainties, however the traditional anti-optimization method is time consuming, and the accurate probability distribution needed for probabilistic optimal method is not easy to obtain. n innovative method of optimization considering design-variable uncertainties, such as ply thickness and orientation uncertainties, and non-design-variable uncertainties such as material property uncertainties is proposed. By including the sensitivities and uncertainties in the modified constraints, a robust optimum design problem is formulated. Besides being used to determine the most appropriate direction in the optimization algorithm, the sensitivities in the modified constraints are also served as the media to evaluate the effects of manufacturing uncertainties. In the proposed approach the numerical method is still needed for the optimization sub-problem, however the anti-optimization sub-problem is analytically rather than numerically solved. It is therefore more efficient in computing time than traditional anti-optimization technique where both optimization sub-problem and anti-optimization sub-problem are numerically solved. A beam-like composite laminate with analytical solution was used to verify the accuracy of the proposed method. The proposed method was then used to perform the robust optimal design of complex laminate structures including holed and non-holed laminate with stress and stiffness constraints, laminate with thermal buckling constraint, and fiber reinforcement composite cylinder with metallic liner subjected to uniform pressure and local loads. he influences of ply thickness and orientation uncertainties and material property uncertainties on optimal weight were surveyed. The most significant effect of material uncertainty is found for the holed laminate plate, and the most significant effect of ply uncertainty is occurred for laminate plate with thermal buckling constraint. Thickness and allowable strain of metallic liner are the other two factors affecting the optimal weight of the fiber reinforcement composite cylinder with metallic liner. If the allowable strain of composite layer is less than that of the metallic liner, the metallic liner should be kept as small as possible to obtain an optimal design, and the optimal thickness of metallic liner occurs at a particular value other than very close to zero if the allowable strain of composite layer is larger than that of the metallic liner.
Subjects
Composite material
optimal design
laminate plate
uncertainty
Type
thesis
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